Fuel and air mixing unit for burner assemblies



March 2, 1954 J. L. MaCFARLANE 2,670,788

FUEL AND AIR M IXING UNIT FOR BURNER ASSEMBLIES Filed Oct. 10, 1949 3Sheets-Sheet 1 Jahn L. Mac Farlane ATTORNEY March 2, 1954 J. M FARLANEFUEL AND AIR MIXING UNIT FOR BURNER ASSEMBLIES 3 Sheets -Sheet 2 FiledOct. 10, 1949 INVEN TOR. L. Mac Forlone John 4 niv d=22; AI

ATTORNEY March 2, 1954 MacFARLANE I FUEL AND AIR MIXING UNIT FOR BURNERASSEMBLIES Filed Oct. 10. 1949 3 She'ets-Sheet 3 VIII/14m v M HIN D QE HWNNNW\\\ WN INVENTOR. John L. Mac Furlone ATTQRNEY Patented Mar. 2, 1954EU'EL' AND AIR MIXING UNITFOR BURNER ASSEMBLIES JohnLmMacFarlane;..Pueblo,- Colo., assignor. try The MacMixen-Inm, acorporatiomof Colorado.

Application Obtoberli), 1949, Serial No. 120,579

(01.; lee-11) 1% Claims.

This invention relates to a fuel and ai r'mix.=-

ingunit forburner assemblies which is useful in obtaining acontrolled'heating pattern and efiii cient' combustion.

Many different types offuel and air. mixing? units orburners havepreviouslybeen devised in. attempts to inorease'the 'efiiciency ofcombustion onto-control the flame pattern. Generally most:

of the previous designs have been basedzon'th'e theory thatv turbulenceis essential for the compl'ete-intermixing of" fuel and air and that a.conical flame pattern is most desirable because the hot zones of'the'fiame-are then concentrated. Certain disadvantages-of fuel andairmixing units designed on the basis ofv the foregoing;theoryhavebecomeapparent." One disadvantage: of fiame patternshaving hotzonesis. noted'where the-capacityof original installations'hasbeentincreased? Such increases: in capacitynecessitatethe burning ofadditional fuel which causes an. elongation of the flame pattern tendingto bring the hot' zone 1 of the flame into contact withiz parts? of thethe box or furnace to the consequent: Accordingly burners that:

damageof said'parts. developnahot zone have-not beenusefuloverra widerange: of "flow capacities unless the furnace orr'fireboxwas' speciallydesigned to accommo' datessucha burner;

Insofar as thesmixing ofthe -fuefl and air is" coneerned;. some of "theprevious designs; have attempted by various: means to increase? theamount: ofiturbulen'ce' within thermixingnnitiand; outwardly into thefiame-Fpattern in the belief": that such" increased turbulence'was'necessary to assure thecompletesintermixing of fuel and: air.

As a: result of." the present inventors studies, it wouldinow seemrthat:manyrprevious' devices for mixing: fuel and:' have: actually" created.too" muchturbulence in: the. flow pattern to. assure tliea'completeeintermixingof'the: combustion sup.- portingr-products;

Primarily the complete intermixture of: fuelair is desired to; increase:thes'efiiciency" of combustion. Sincemaximum efliciency'has not been:obtained previously with: prior types of."

mixing: units or burners; it: is..-evidenti that the intermixtureoftfuel and air has been"; incomplete orat least not in .theproperproportions. These inefilcienciesra general-1y occur: at all levels ofoperation, but in most: installations an increase in the percentcombustibl-es" or 'in: excess air: is

notedonv either: side of an optimum. operation condition. Any type. of:burner which? doeszenot' operate v at; near maximum. efficiency I overa; wide range--ofoperationlevelsdces not thoroughly 2: satisfy therequirements and other firebox installations.

In order to overcome the'shortcomings of prior: 7 devices, thepresent-inventor has devised a fuel and airmi'xing 'unit'designed tosatisfy the following: objects:

To provide a fuel and'air mixing unit which efficiently combines fueland-air in readilyad justable exactproportions-toassure efiicientcombastion.

Tdprovide a" fuel and-air mixing unit'- in whichliquid or gaseousfuels-may be eflici'ently intermixed with air" or oxygen. without 1creating ex=- cessive" turbulence within or at the discharge of saidmixing unit.

To providea fuel and ai-r mixing unit which is adapted to give-ahomogeneous flame pattern";

To provide-a fuel and air: mixing unit having a. plurality of successiveexpansion chambers adapted" to intermix the fuel and air products"eificientlybefore discharging said" products in a'homogeneousfiamepattern.

To provide'a fuel and air mixing unit having" diameter adapted toefficiently intermix I liquid and gaseous" fuelswith air introduced intosaid mixing unit by concentrically arranged conduits having flowsuccessive chambers of increasing and: pressure controlling meansassociated'them with. p

're: provide a fuel burning arrangement inclusive: of a mixing unithaving expansion chambers of: successively increasing diameter; conduitmeans for carrying fuel to said mixing" unit :at a predetermined rateof-flow together with furthenmeansfor controlling the amountof primaryair" introduced? into said mixing unit and the-ramountiofrsecondary airintroduced into the fire-box throughachecker preheating system;

To provide a fuel and air mixing unit which: is easily: and"economically rnanuf'actur'ed and whichin'corporates simple controlfeatures. easily I operableiby the personnel maintaining said mix ingunit;

Further: objects and advantagesof the presentinvention will be apparentfrom the appended de scription and drawings in'which:

Fig. 1 is anelevation'inpartial section'sh'owing the general use ofthemixing unit of this inven-' tion 'in'a' brick kiln' fire box'installation inclusive-'- of a secon vlary preheating system;

Fig. Zis an el'evation in partial section showingthe features of anembodiment of this invention inexact detailxdrawn to scale;

321's an elevation in partial section. showing I the'details offaifueland'air conduit arrangement" of modern furnace; .kiln:

together with air control means for association with said mixing unit;

Fig. 4 is an elevation in partial section showing the features of aseparate embodiment of this invention in exact detail drawn to /3 scale;

Fig. 5 is an elevation in partial section showing the details of aseparate embodiment of the fuel and air conduits arrangement togetherwith the control means thereof; and

Fig. 6 is an elevation on a reduced scale taken along the lines 66 ofFig. 4.

Briefly stated the present invention provides a fuel and air mixing unitinclusive of an entrance chamber having side walls which narrow orconverge to provide an opening of minimum diameter consistent with theflow capacity of the mixing unit. Downstream from the said entrancechamber and the opening therein, a plurality of expansion chambers ofsuccessively increasing diameter in the downstream direction areprovided. "Each of the expansion chambers is substantially cylindricalin shape having the individual lengths thereof greater than thediameters of said chambers, but each of said chambers being ofsuccessively decreased length with respect to the next adjacent upstreamchamber. The chambers themselves are separated one from another by aplurality of restrictions formed on the inner surfaces of said chamberswhich tend to narrow the passage therethrough to provide openings ofdiameter less than the diameter of the next adjacent upstream expansionchamber. Further these openings are of successively increasing diameterin the downstream direction. By means of the foregoing arrangement theinventor is able to establish a flame pattern which is homogeneousinsofar as the dispersion of color is concerned. By use of separatemeans for controlling the amount of atmospheric air, fuel and air underpressure introduced into the mixing unit, the amount of fuel and airintroduced can be controlled in exact proportion to maintain highlyefiicient combustion. Separate arrangements for controlling the amountof fuel and air introduced are provided in accordance with thisinvention together with means for controlling the distribution of theaforementioned homogeneous flame pattern within a fire box, furnace orthe like.

In Fig. 2 the details of a first embodiment of this invention are shown.In this figure it will be noted that the inventor provides a fuel andair mixing unit H having in successive downstream arrangement anentrance chamber !2, a

first expansion chamber [3, an intermediate expansion chamber 14 and alast expansion chamber I6. As shown, the entrance chamber is providedwith converging side walls I! of substantially frusto-conical shape.These side walls 11 converge or narrow in the downstream direction to anopening l8 of minimum diameter consistent with the desired maximumvolumetric flow for the particular installation. Beyond the opening 8 afirst expansion chamber 13 having walls [9 of substantially cylindricalshape is disposed, and interconnecting the cylindrical walls B9 of thefirst expansion chamber 13 and the converging side walls l! of theentrance chamber I2 is a section 2| of expanding diameter to provide atransition member between the opening is and the cylindrical walls 9.The length of the first expansion chamber 13 and of the walls I9 thereofis approximately twice the inside diameter of the expansion chamber #3.At the terminal downstream end of the first expansion chamber 43, aconstriction 22 disposed upon the inner surface of the walls 19 isprovided. Preferably the constriction 22 narrows the passage through thefirst expansion chamber 3 to provide an opening 23 of diameter greaterthan the opening 58 and less than the diameter of the upstream expansionchamber it. An intermediate expansion chamber likewise having walls 24of substantially cylindrical cross section is disposed downstream fromthe opening 23 and is interconnected to the chamber 43 by a continuationof the restriction 22 and expands in diameter from minimum size at theopening 23 to maximum size coterminous with the diameter of the chamberM. The diameter of the intermediate expansion chamber i4 isapproximately 10 to 25 per cent greater than the diameter of the nextadjacent upstream expansion chamber 13, and the length of theintermediate expansion chamber i4 is approximately one and one-halftimes the diameter.

At the downstream end 01 the intermediate expansion chambers anotherrestriction 26 is likewise provided to narrow the passage through saidintermediate chamber M to provide an opening 2? of diameter greater thanthe opening 23 and less than the diameter of the intermediate expansionchamber M. A third or last expansion chamber 46 having cylindrical walls28 is provided downstream from said opening 21 and a continuation of therestriction 26 of expanding diameter interconnects the intermediatechamber I l and the walls 28 of the last chamber [6.

The diameter of the cylindrical expansion chamber it is approximately1.2 times the diameter of the intermediate expansion chamber l4 and thelength of the last chamber I6 is approximately 1.2 times the diameter.At the terminal end of the last expansion chamber It a circularly formedrestriction 29 is provided which narrows the passage through said lastexpansion chamber to an opening 3|. The diameter of the opening 31 isgreater than the diameter of the upstream opening 27 but less than thediameter of the adjacent upstream expansion chamber [6.

Besides the ratios and proportions already set forth, it should be notedthat the successive openlugs 18, 23, 21 and 3! are of successivelyincreasing diameter in the downstream direction. The expansion chambersare of successively increasing diameter in a downstream direction fromthe entrance chamber I2 and of successively decreasing length. In allinstances however, the sizes of the openings 18, 23, 21 and 3| are ofsmaller diameter than the next adjacent upstream chamber. While specificratios and proportions have been set forth, it should be apparent thatmodification within certain limits is possible. Accordingly it should berealized that the dimensions and proportions set forth are given only toenable others to readily practice the present invention.

As further shown in Fig. 2 a mixing unit I l is preferably used inconjunction with apparatus for delivering gaseous fuel into the mixingunit Where a plug is used, an orifice rma 3111s;dri-lledfthmuggrtheapluggfltsathanthe: gasseeouszfuelbeingcarriedpwthecconduitfi2-2iss.deepliveredflhroughrthe orificeiflintosithepentrance plish suchadjustedzpositioningcyofi the-rairtcontrol:disk 39; the :inventor. in thgelnbodiments; shown.

provides threads: 4 l :of: extended :length; cutin.;the.-.outersurfaceof the pipe "32;. The air: control disk. 39 is preferably amember having a flat disk shape;- OffISiZQ larger than the entranceopening: :38 and a.boss.=42. The bossa42' and the centra1. portion: ofthe disk 39 is; provided withv an. opening; 4-3 having threads Mthereinforzmating engagement with;.the threads 4|, on. theexternaLsurface-of;

the pipe'32. It willJloenoted thatxas .th'esfiil control disk 39. isrotated With-respecttothepipe- 32 it willrbe moved: inwardly.orroutwardly with respectztothe entrance opening 38.: When the disk'ismoved away-from the entrance .opening- 38: the. :openingAii ofcylindrical shape betweenthes disk.39 ancLtheentrance opening: 38 .will'be;in-. creased .to.:;a1low an. increasednamount 10f; air: to" flow"into, the .2 entrance sectiomfl. of: the mixing-:. unitl l..

In. Fig. 1 a; typical .insta1latiorr: which fully:

utilizes the advantages: ofya. mixing: unit .similar. :1

to'that shownjn Fig, 2;iis shownzz. Inthisfigure itswill be seenthat-the:iuelJand-air mixing-unit ll is supportedby astand 4! S0,tha't:thB"dOWni"' stream opening 3!. irrthe last: expansionxchame her:I 6 -.discharges through an opening-- 48 ;in the; exterior; wall .49of:a:. fire box 51.: The conduit. 32 is interconnected.with;a:.fuel;suppl-y pip.er;52;:. and a .valve: 53 previouslymentionedisrprovide'd to control theaflow ofzffuelinto"arnhathroughtthe conduit32.v Beyondthe .valvefifi in a downstream: direction: the. conduit32.:is; provided;;with;.;a1tap:

determining and:. COIItIOiHIlgfthGi delivery. pres? sure: ofthe gaseousfuehbeingusedr. Asprevious-i- 1y. explained the 7 air; control .disk 391 is". mountert" foriadjusteol movement .alongsj the. conduitziifltita:vary "and. control the amount of primary: air

troduced into.- the mixingunit l'l-.. The firerboxz itself which. is-vinztthis.figuretshown;;as:beingrsensclosed withinraki-ln 58isprovided:with a grate 5.9. and-a mass of broken firesbrickrfitli onother simize larmaterial .Whichseparates the firehoxrilrfromt.

a secondary ainentranceichannelA62. 'Ifhetc'ham nel 162::isconnecteclrwitha: headen:63. wlnclnissinte terconnected to aconventionaltypesetblower (not shown) so that secondary air: willgbeainr-u troducedinto thew-fire b'oxfil: through the header 63 and. channel 82- andupwardly:throughr the: broken brick 6! and gratex59- to-further controlthe placement of. the flame pattern: within: the? firebox 51 and topreheat-the secondary air by" means of; its passage through. the;checker-like;

system provided; by the. broken brickixfil; Bye" means of this.arrangementzwhen the5 amount of 1; fueLand air,introduced;throughntheimixinggunita:

I l:.-iseincreased',; the dilemma;patterntaemittinge frmnzv thedischarge opening ,3 I 1; can be econtrollediso that.:.;it:wil1;notrimpinges-upon, the flrer N with such-intensity? as to.;.destroyg; thefire waih; Sincetheefiamewpattern emitted by. the

unite Ill; issubstantially;homogeneousainichara tenandt. since r=there;;are 'no.--marked'lhot'. zones thecfla'me pattern.thiscontrolsot;.theplacemenh of-thafiamepatterniis;possibleaWithoutendangera.ingany;ofrthecothenparts,.suchcasitherrooilnoirs burner: the placement:of, the: flame pattermcam be? controlled? in: .furnaces, ;ovons; openheartbeat; soaking pits .and-thehke to preventtheedestructiOIisIOfiQfiTtSaWit-hifiaSliCh; unitsxduemto: theasconecentrationzofrheat:

The exact character: ofithe'fiamepatterntemitn tediby the. mixing. unit;H should-perhapsbemomi fully: describedr It has-been:writtenrthatnthiss' flamezpatternciszhomogeneousc. By this-termrthezz AP inventor :intendsl'to l. convey the .impressiomthatn.

there;are;-.no marked. physically; 'apparentzdemar cationsofiffiamezpatt'ern which'mightbtncmrac terizedzas oxidizing; reducing,OI asrarhotzgzoner Insteadn-then flame remitted; from; the idisehargeiiopening-113d; is: of elongated: substantia'll'ypyline dricai-ushape orslightly increasing diameterawayrfromrthe. discharge opening-:31;Thronghouttheis visible zportion of tthe. flamev patterntheintemnixeturez-oicolorsz such .asa':.the:.-.characteristic reds'r. bluesgreens etc;- isz'evemuor other words;.the;i-;

flame pattern iShOmOgBIIEOHSISiIICEthE5diSpe1ZSmI!5- of suc'hcharacteristic colorsais complete-.2;

While; theev complete. dispersion 10f: flameecolorsaz' iSiHGtCOIIClUSive to. iprove .=that there isza compiete inten'nixture .ofi fuel" andair, such results: coupled? with flue gas analysis:resultshowing:a-maximum:

eifici'enoy: area. conclusive; to @show: that thee-inten mixtureaccomplished; by the inventor's i type--o1.:5v mixing unit is completeand may -be-regnlated inzexact 'proportion-toestablismmaximum comebustion: efli'ciency: Inc a brick kiln-z installation; thisstypeP-ofmixing unit": has made-it-possible to:

obtain consistentresults showingnot over of -1 per-:cent:'excess:-oxygen with no combustibles inra the flne gas analysis. In the sameinstallation":- mentionedj when mixing units of i the describer i typeare installed, the saving inafuel was' hetter than: 48 per cent; andsince a more intensee heair waszpossibles in a shorter period "of" timethe-:pro-r ductiorr capacity of'the plant was-increased nnd...

the fiiel 'cost per thousand-bricks waseffective y cut-in: halt-. Whileit" is admittedthatthes resu'l t's are-perhaps unusual; they are-evidence ofi thepossibilitiesinherent in the ainventor s type=of-desi'gn. i

Bsidesthegaseous-flxel an d air 'installationiasz shown in-Figsz- I and2 it has :ibcerr found that: the=present type---of mixing unit isadaptablei't'o oti'icrifuel burning applications. Actually unitsofdesignsimilar-to that -desc-ri-bed' have been 1 used? to interrnixgaseous;liquid and-"solidfuels air linden-pressure and-at atmospheric pressu In:all instances theresults have shown-thatthe fuel= and airintermixtureobtained is suitable fom the attainment of maximum ornearvmaximuma combustion eflicienciese arrangement for theefiicientintermixtu-re of -gaseons and liquid fuels' with air under pres-)-sureand at atmospheric pressure is=.-showrr in- Fig-2'3; In this-figureamixing unit H is pro' vided of: f orm-.::andr shape substantiallwas 5.shownrr.

in Fig. zahayingzamentrance chamber; l ZLandQanr entrancen. opening?335i asc previously" described?Thtzeazseparatez;concentriczconduitstaarearranged withinon'adiacentztozthe entrance seetiomofzthega shown): of;-..the;:kiln-.Likewise:withithisstyype:air.

mixing unit H so that a gaseous fuel such as natural gas, a liquid fuelsuch as fuel oil and primary air under pressure will be conjointlyintroduced into the entrance section l2 on passing through a nozzle 56having an orifice 61 therein. The actual arrangement of the conduits andassociated members is fully shown in Fig. 3 where it will be noted thatgas is introduced by means of a pipe 68 into a T fitting 69. A gasconveying conduit H interconnects with one opening of the T to form theoutermost of the conduit members. The outer surface of this conduit H isprovided with threads 72 for the reception of an air control disk 39 ofshape, size and purpose corresponding to that previously described. Asbefore, movement of the control disk 39 toward or away from the entranceopening 38 decreases or increases the amount of air introduced into theentrance chamber l2 at atmospheric pressure. A tapped plug 13 isprovided in the third or remaining opening of the T fitting, and aconduit 14 having an outside diameter that is less than the insidediameter of the outer conduit ii is connected through the tapped plug 73and disposed concentrically within the outer conduit H so as to providea passage it through which the gas introduced into the T by the pipe 58may be conveyed toward the orifice opening 61. One opening of a second T'11 is interconnected to the outer end of the conduit '74 and an airdelivery pipe i8 is interconnected into another opening of the T ll. Atapped plug 79 is disposed in a third opening of the secondT H and aninner conduit 8! is connected through the tapped plug 19 and disposedwithin'the conduit 14 to convey oil to the orifice 61 and into theentrance section l2. The outside diameter of the conduit BI issubstantially less than the inside diameter of the conduit 74 so that apassage 82 is provided between the conduits 8i and 74 through which airunder pressure may be introduced for passage to and through the orifice61 and into the entrance chamber 12. This particular arrangement of feedconduits is advan tageous in installations where a more intense heat isdesired or where the supply of one or the other types of fuel is notthoroughly dependable. Where a more intense heat is desired both theliquid and gaseous fuel will be introduced simultaneously with air underpressure and air at atmospheric pressure to provide a homogeneousmixture having a high heating value. It is significant that theintermixture of the separate types of fuel is so complete that theresulting flame pattern is still homogeneous and the flue gas analysesshow corresponding eificiencies. By the use of valve members on theseparate pipes 68, i8 and illthe flow of any of the separateconstituents may be closely controlled and accordingly whenever it isdesired or necessary to out 01? one particular type of fuel, adjustmentmay be readily made to maintain the efficient combustion. In instanceswhere the primary type of fuel is cut off, the provision of a secondaryfuel which may be eihciently burned to maintain a satisfactory heat isinvaluable.

In Fig. 4 a modified form of mixing unit construction is shown. In thisfigure the mixing unit ii is provided with an entrance chamber I2 and aplurality of expansion chambers 13', M and 15'. As in the previousarrangement the expansion chambers are successively of increasingdiameter in the downstream direction. Further the side walls ll of theentrance chamber [2' narrow to provide an opening I8 at the mini mum'diameter of said entrance section. The

walls 19' of the first expansion chamber l3 are substantiallycylindrical in shape and a section 2! of expanding diameterinterconnects the opening 18' With the walls IQ of the first expansionchamber 13. Adjacent the downstream terminal end of the expansionchamber IS a restriction 22' is disposed to provide an opening 23' ofdiameter smaller than the diameter of the expansion chamber IS. Theactual form of the restriction 22 is difierent than that illustrated inFig. 2 inasmuch as the modified form of restriction 22' provides for agradual and even reduction in diameter from a maximum size equal to thediameter of the expansion chamber E3 to a minimum size equal to thediameter of the open ing 23'. Downstream from the opening 23 therestriction 22' has an expanding or flared internal diameter adapted toprovide a smooth but relatively sharp transition from the diameter ofthe opening 23 to the internal diameter of the walls 24' of theintermediate expansion chamber 14'.

A restriction 2G is likewise positioned adjacent the downstream terminalend of the intermediate expansion chamber Hi. The construction of therestriction 25' is similar to that of restriction inasmuch as itprovides for a gradual reduction in internal diameter from the diameterof the walls 23' to the diameter of an opening 27 sepa rating theintermediate expansion chamber M from the last expansion chamber l-S.Downstream from the opening 2? the walls of the restriction have anexpanding diameter to eifect a smocth but relatively sharp transitionfrom the diameter of the opening 2? to the internal diameter of thewalls 28 of the expansion chambcr jacent the downstream terminal end ofthe ex pansion chamber E5 to narrow the passage therethrough and toprovide a discharge opening 3 l of diameter less than the insidediameter of the walls 23'. Restriction 2%)" is formed similarly to therestrictions 22 and 2 8 inasmuch as its walls are adapted to provide agradual transition between the diameters of the external walls 28 andthe discharge opening 3! As in the previous embodiment the diameter ofthe expansion chamber 5 3 is greater than the diameter of the openingl8. Further the expansion chambers l3, i i and it are of successivelyincreasing diameter in the downstream direction and the diameters of theopenings i8, 23', 2'! and 3E are likewise of successively increasingdiameter in the downstream direction. Again each of the separateopenings 18, 23, 2'! and 3| are of less inside diameter than the nextadjacent upstream chamber. between the embodiments shown in 2 and Fig. 4are concerned with providing transition shapes between the separateexpansion chambers that more nearly conform to the shape of conventional type nozzles. These change have been made inasmuch as theembodiment shown in Fig. 4 is designed for larger capacity than thatshown in Fig. 2 and for the larger flow capacities the nozzle typerestrictions give the proper intermixture without establishing excessiveturbulence.

Figs. 5, 6 and a portion of Fig. 4. show the details and arrangement ofa separate type of fuel and air feed and control. In Fig. 4 it will benoted that the entrance end 83 of the mixing unit H is provided with aflat face 3 and the side walls ll of the entrance chamber l2 are turnedto provide a cylindrical face 88. These machine faces are provided sothat the'y'may be 3 A further restriction 23' is disposed ad-Essentially the differences securely engaged.- in cooperative mating"surfaces fi l ofaspidermember Si}: As shown-in Fig: 6 the spider8'8is"provided withan outer ring-8% having-the aforementioned matingsurfaces 8? cut'on-the inner face thereof. Wehmembersi interconnect acentral huh 9'2 I witlr'the ring" 89 so-as to provide opening'sflBcommunicating with the-entrance chamber 32'". set soreu are the ring 89are adapted to"secure-thes .ormemhe'r 88 to the mixing unit '1 i andth-ehub 81? provides an opening fi l in-whicltthefuel and feed con duits arereceived.-

A- separate arrangement for the fuel and air feed conduitsisshovrniwFi'g'. Fran-d iir-porti'on ofFig. 4 where it willaga-inhenotedthat the applicant providesa plurality of concentric con duits'liii,9'2" and steer introducing oil respectively into the entrancechamberorthe mixing unit l I. The outermost "oi "the conduits 98" is' supportedin concentric positionwithin the entrance champ-swi liythe spider-8S?and its inner end is provided Winn-threads Be te-receive areducer-member let, the outer-end of which is partially "closed-myapl'ug Ioil' hav'ingan orifice opening los therein: Anin the previousembodimerit; adjusting threads los -areprovided-"on the outer surface ofthe conduit- SB- for engagement by the threads -'-I ii 'of -thea-ircontrol-disk 39. By means of this arrangement "the air control disk 39*may b'emoved to-"adiiusted position alcng'the conduit SS' tQ'increase-ordecrease the 'cross=sec-'- tional aren of flow past the air control*di-slc 3-9" and-the spider os andinto'the entrancechamber l 2Accordingly a correspondingly accurate control of the amount oiatmospheric-air introduced into the mixin'gwunit is liltewise possiblein this embodiment.

The outer end lot-"the conduit 96 is-secureei *in one opening'of-acrossI Mgassupply'pipe I 9 5 having a valve I It! thereon ion the control ofgas through the-pipe -I fiE- is secured in a -second open in 'gof thecross l $5 in such manner -that the gas introduced-- thrOugh the-pi-peI0 8" will now di rectl-yinto the cross 1 I Gi -and through a passage I08' between the conduits' fi t -and 9-1 into the en trance chamber-42Conduit-t-T whichds diep'osed concentrically within conduit e-tiis heldin suchconcentric position' by a tappedplug I Se im a-third opening ofthe cross m5, Theairflowing through the Z1 conduit 91, however; I is:ntrocluced through .afipipe-I I I passing through p eapmg I I2'disp'osed 1 the-fourth openingthe: cross; lE ipev I I I l is clikewiseprovidedwith a1. valve: I I3 adapted :to control the amount of aintroduced through :the pipe-I l I andithrough :amassage l I t betweenthe ccnduits 9 1 and 982mm the entrance chamber: I2 1. In orderito malzethis arrangement possible the'lpipe II I is threaded sin-to a .Tisection I I6 welded-atright angles to theconduiteil: The outerend of theconduit e1 has a reducer; i I i socured thereto, and conduit 98.is-threaded for passage through the-smaller enclof the reducer: I IT. AvalveI 1845 provided on the concluittamo control the flow of oil:through the conduit-V 9B; through-a metering. orifice I disposed in.theinner end of the conduit-Q8 and into .theentrance chamber I2'-.

By, means of. the fueliand air flowicontrol are rangemen-t lastdescribed; the. inventor is able to. control the exact proportions offuel -and-v air introduced into the mixing unit II'-. With such controland with. theintermixing; features of: the mixing unit I I .the inventoris ableetomainta-m highly; efficient combustionhaving-gthe advantagespreviously described:v

The high level of efficiency possible with mixing unit's-madeaccordingto-the designs of the present invention-is indicated by the-following data of mixing units similar to those shown in Figs.- land 2"in a conventional silica fire brick Uakineoperation. Inone specificinstallation a; b'rick kiln having an inside-diameter of approximatelyfeet: was provided with eightmixing units substantially as shown in lies? 1 21 16 2. This==down draft periodic type ofkiln"having a capacity'of-'approximately190,990"- nine inch fire brick was chargedto capacityandsealed. For the first n-inety-'six* hours themixingunit I -'I wasprovided 'with an orifice =3i having an op'ening of-an inch diameter.During-.thefirst twenty four: hours th'e m-ixing unite -were operatedwith a 6 ounce pressure on the natural gas feed. With the -air control38 ad5'usted to give' eificient combustion approximately 75,000-- cubicfeet of gas were used and-a temperature-of 660 was attained atthe end Iof thetwenty four ho'iir l1our' period-.- For the next twenty-fourhour's-12 ounces cf 'ga's -pressur'e was-used anclcorrespond ingchahg'eswere n'ia'de-in the positioning of the air control disk to 1assure-complete combustion of tl ie greateramount of fuel. Duringthissee ond twenty=four'= hour periodapproximately 123,00'0 cubic feet ofgas were usedand a tem perature of l320- F5 was obtained Duringthe=tnir-d-="twenty-rour hour period i 20 ounce's'of pressure was used'" onthe-'gas -supply-"ahd the amount of primary air was increasedto givefiicient combustion. During th-is third twentyfou-r' hour-p'eriodapproximately" -163g000cubic feet of gas-was-burned-am a=tempereiture ofapproxi mate1y'2,000- E. was obtained; Durin'gthe fourth twenty-fourhour period,-'four pounds;- four-ounces gas pressure was utilized" toburn approximately 3l7',000cu'bic=feet of gas-bringing the to-atemperature -ofapproximately-2400 F5 After ninety sh'shours "elapsedtimethe orifice 31*Waschangedto provide an opening --of an inchin diameter:Withthis-"orifice"size; two pounds, four ounces of gas-pressure--was"used" for thenext twenty fourhours-toburn approXi-mateiy4421500 cubic'feet of gas and to obtain atemp'erm ture ofapproximately-"265W After atotal elapsed time of hours the gas-pressurewas increased-to*threepoundspersquareinch for a period of twentyfour'hours-- during" which time approximately 511E000 cubic feet of" gas wasbu-rnet'l'. At the end-of this lasttwentyefourhour period =a--temperature of-2'750' F. had been obtained'withinthekiln: As "soonas-this tempera ture was obtainedthe gas supply--was cut off andthe-"bricks" were ieft inthe =withoutad'ditional neat-for fourteen days.

During tl'ie-"entire heating cycle a total of approximately1,-63ZJJGO-"cubicfeetbf gaswa'sburned-i In connection with-these totalfigures it should lie-noted that-thekiln installation mentioned waslocated at analtitudeofaproximately Mme-feet and the heatingvalue ofthe'natural gas used wasfnecessaril'y; reduced by such" conditions:

Fromth'e foregoing figures when 'taken'to'gether with results.reviously; mentioned it should. be apparent that the; present device.fulljif satisfies the objects enumerated. Whileseparate embodi' ments.of this invention have beenshownland ide scribed, it.isrreaclilyiapparent that the invention is -adaptable-.to modifications-andchanges.All such modificationsand .changes-asarea-within. the scope of; thehereunto: appended: claimsare deemed toizbe apart of this invention:

. What is claimed is:

1. A mixing unit for burner assemblies comprising an elongatedopen-ended body having an entrance chamber inclusive of side wallsforming a narrowing passage arranged to receive streams of air andfuel,- means for injecting streams of air and fuel into said entrancechamber at its open end, said body including a plurality of expansionchambers of successively increased crosssection downstream from saidentrance chamber, and a plurality of constriction members between saidchambers having surfaces arranged to narrow the passage therebetween toa cross section less than the cross sectional dimension of the nextadjacent upstream chamber so as to mix said streams in their travelthrough said chambers.

2. A mixing unit for burner assemblies comprising an elongatedopen-ended body, anentrance chamber on said body inclusive of side wallsforming a narrowing passage arranged to receive streams of air and fuel,means for injecting streams of air and fuel into said entrance chamberat its open end, said body including a plurality of substantiallycylindrical expansion chambers of successively increased diameterdownstream from said entrance chamber, and a plurality of restrictionsacting as division members between said chambers having surfacesarranged to narrow the passage therebetween to a diameter less than thediameter of the next adjacent upstream chamber so as to mix said streamsin their travel through said chambers.

3. A mixing unit for burner assemblies com prising an elongatedopen-ended body having imperforate side walls, an entrance section onsaid body arranged to receive streams of air and fuel, means forinjecting streams of air and fuel into said entrance section at its openend, and said body including a plurality of expansion chambers disposedin open ended relation lengthwise of said body downstream from saidentrance section, each of said chambers being defined by restrictionsacting as division members at the ends thereof, each said expansionchamber being of shorter length than the next adjacent upstreamexpansion chamber so as to mix said streams in their travel through saidchambers.

4. A mixing unit for burner assemblies comprising an elongatedopen-ended body of circular cross section, an entrance section on saidbody arranged to receive streams of air and fuel, means for injectingstreams of air and fuel into said entrance section at its open end, andsaid body including a plurality of expansion chambers disposed in openended relation lengthwise of said body downstream from said entrancesection, said chambers being separated from each other by a restrictiontherebetween, each said expansion chamber being of greater diameter andshorter length than the next adjacent upstream expansion chamber so asto mix said streams in their travel through said chambers.

5. A fuel and air mixing unit for burner assemblies comprising anelongated open-ended body having an entrance section inclusive of sidewalls forming a narrowing passage, said body including a plurality ofexpansion chambers of successively increasing diameter and decreasinglength downstream from said entrance section disposed in open endedrelation lengthwise of said body, said chambers being separated byrestrictions therebetween, a conduit for conveying fuel having adischarge outlet disposed within said entrance section at the open end,an

orifice member mounted at said outlet in heat conductive connection withsaid conduit, an air control disk mounted on said conduit at the upstream end of said entrance section for selective movement along saidconduit to vary the quantity of air introduced into said entrancesection, and valve means on said conduit for controlling the amount offuel introduced through said conduit into said entrance section.

6. A fuel and air mixing unit for burner assemblies comprising anelongated open-ended body having an entrance section inclusive of sidewalls forming a narrowing passage, said body including a plurality ofexpansion chambers of successively increasing diameter downstream fromsaid entrance section disposed in open ended relation lengthwise of saidbody, a first conduit having a discharge outlet disposed in the entrancesection for discharging gaseous fuel into the upstream end of saidmixing unit, a concentric intermediate conduit disposed within saidfirst conduit and having its discharge outlet within said first conduit,an inner conduit disposed concentrically within said intermediateconduit having its discharge outlet within said intermediate conduit,said inner and intermediate conduits providing a passage for theintroduction of air, a regulating member having an orifice openingtherein for engagement with the discharge outlet of said first conduitfor regulating the flow of fuel and air into said mixing unit, and valvemembers on each of said conduits for regulating the how and pressure ofthe fuel or air in the respective conduits.

7. A fuel and air mixing unit for burner assemblies comprising anelongated open-ended body, an entrance section on said body inclusive ofside walls forming a narrowing passage, said body including a pluralityof expansion chambers of successively increasing diameter downstreamfrom said entrance section disposed in open ended relation lengthwise ofsaid body, concentric external, intermediate and inner conduits ofselected diameters arranged to provide a passage between said externaland intermediate conduits and a second passage between said intermediateand inner conduits, with a third passage internally of said innerconduit, said conduits having their discharge ends disposed in spacedrelation to the downstream end of the entrance section of the mixingunit to convey liquid fuel, gaseous fuel and air under pressure intosaid mixing unit, an air control member for selective positioning tovary the amount of atmospheric air introduced into said entrancesection, and means for separately varying the pressure head on saidliquid fuel, gaseous fuel and compressed air to maintain a regulatedflow of said fuels and air as necessary to obtain efficient combustion.

8. A fuel and air mixing unit for burner assemblies comprising anelongated open-ended body, an entrance section on said body inclusive ofside walls forming a narrowing passage, said body including a pluralityof expansion cham bers of successively increasing diameter downstreamfrom aid entrance section disposed in open ended relation lengthwise ofsaid body, concentric external, intermediate and inner conduits ofselected diameters arranged to provide a passage between said externaland intermediate conduits for gaseous fuels and a passage between saidintermediate and inner conduits for air under pressure with a thirdpassage internally of said inner conduit for the flow of liquid fuel,said conduits having their discharge ends disposed caverns inspacedrelation to the dcwnstreamrendiotfthe entrancersection; tosconvey fuels:and air into said unit, a nozzle in the end of said externalcondfiitdor. controlling theflow of. said feels. and air: externalthread's"on"the outer'surfa'ce of. said external conduit; an aircontroi" disk? mounted onsaid' threads" for selectivepositioning, T011said conduit to vary the amount of? atmospheric? air'introducedi'into'saidentrancetsection, and meansforfseparately'varyingthe' pressure headionsaid liquid: fu'ei';gaseousfuel and compressed? air'to maintaina' regulated-flow OfISEtidfuelsand air asnecessary to obtainefiicientwombustion;

9; Affuel' and air mixin'g'nnit for burnerassemblies comprising anelongated open-cnded b'ody, an" entrance section on said*- bodyinci'u'siveof side walls forming: a.-narrowing:;passage and an openingsof minimum diameter consistent. with the flow requirements-of -'tlfe.mixing unit; means forxinj-ecting. streams air andifueliinto saidentrance chamber at=itsiopen..end, said body forming}v alplurality of"expansion.. chambers,,,including a first expansion chamber disposeddownstream from said entrance section of substantially cylindricalshape, a second expansion chamber downstream from said first chamber ofsubstantially cylindrical shape having an internal diameter greater thanthe internal diameter of said first expansion chamber, a third expansionchamber downstream from said second expansion chamber of substantiallycylindrical shape having an internal diameter greater than the internaldiameter of said second expansion chamber, constriction members betweensaid chambers having surfaces arranged to form passages between saidchambers having a diameter less than the diameter of the next adjacentupstream chamber, and a constriction at the discharge end of the last ofsaid chambers providing a discharge opening of diameter less than thediameter of said last chamber and greater than the diameter of thepassage through the next adjacent upstream constriction member.

10. A fuel and air mixing unit for burner assemblies, comprising anelongated open-ended body having an entrance chamber open to theatmosphere, said body including a plurality of expansion chambers ofsuccessively increased cross sectional area downstream from saidentrance chamber, a plurality of constriction members between saidchambers having surfaces arranged to form passages between said chambershaving a cross section less than the cross section of the next adjacentupstream chamber, and a conduit means for delivering fuel into saidentrance chamber for subsequent mixing during travel through the mixingunit.

11. A fuel and air mixing unit for burner assemblies, comprising anelongated open-ended body having an entrance chamber, said bodyincluding a plurality of expansion chambers disposed in open endedrelation lengthwise of said body of successively decreasing lengthdownstream from said entrance chamber, said chambers being separated bya constriction therebetween, and a conduit for delivering fuel and airto a point of discharge into the entrance chamber of said mixing unit.

12. A fuel and air mixing unit for burner assemblies, comprising anelongated open-ended body having an entrance chamber open to theatmosphere, said body including a plurality of expansion chambers ofsuccessively increased cross sectional area and decreased lengthdownstream from said entrance chamber, a plurality of constrictiorfmembers lietweerr saidschamhers having surfaces arranged o formpassages-fibe tween said chambers having a cross I sectional area lessthan the crossssectional area of the next adajz'tcent upstream chamber;and :a -conduitzifor delivering air an'dz fuel into. the first upstreamchamber of said mixing 13. A mixing unit for burner assemblfesscomsprising an elongated'bpen body havirtgzimperferat'e sid'e walls;-anentr-ance *sectionnon' said lbody arrangedto"receivestreams of=airandfuelt means fen irrj ecting' streame= of fair and fuel: intonsaidentrance:section'at its open' end; said-bod y-formr ing a piurality ofexpansion chambers, including, a first expansion chamber' downstreamfromasai d entrance section; a: second expansion chamber dc nst'ream-*-fr0mz1 saidifirst expansion :chamber =reater ntern'alcrosszsectitirrthantsaidifirst chamber; a this expansionchamber down stream H fromsaidsecondi expansiorr chamber: of greater cross section dimension thanthe internal cross=--'sectibn ofsaid second chamber, and restrictionsacting as division members between said chambers having surfacesarranged to form passages therebetween having a cross section less thanthe cross section of the next adjacent upstream chamber so as to mixsaid streams in their travel through said chambers.

14. A mixing unit for burner assemblies comprising an elongatedopen-ended body of circular cross section having an entrance sectioninclusive of side walls forming a narrowing passage arranged to receivestreams of fuel and air, means for injecting streams of air and fuelinto said entrance section at its open end, said body including aplurality of expansion chambers of successively increased diameterdownstream from said entrance section, and a plurality of restrictionsacting as division members between said chambers having a diameter lessthan the diameter of the next adjacent upstream chamber, said passagesbeing of successively increasing diameter downstream from said entrancesection so as to mix said streams in their travel through said,chambers.

15. A mixing unit for burner assemblies comprising an elongatedopen-ended body having an entrance section inclusive of side wallsforming a narrowing passage arranged to receive streams of fuel and air,means for injecting streams of air and fuel into said entrance sectionat its open end, said body including a plurality of expansion chambersdownstream from said entrance section, and a plurality of restrictionsacting as division members between said chambers having surfacesarranged to form passages between said chambers having a cross sectionless than the cross section of the next adjacent upstream chamber, saidpassages being of successively increasing cross section downstream fromsaid entrance section so as to mix said streams in their travel throughsaid chambers.

16. A mixing unit for burner assemblies comprising an open-ended body ofcircular cross section, an entranc section on said body inclusive ofside walls forming a narrowing passage arranged to receive streams offuel and air, means for injecting streams of air and fuel into saidentrance section at its open end, said body in-v cluding a plurality ofexpansion chambers downstream from said entrance section of successivelyincreased diameter, restrictions acting as division members between saidchambers having surfaces arranged to form passages between the chambershaving a diameter less than the diameter of the'next adjacent upstreamchamber, and a constriction at the discharge end of the last of saidchambers providing a discharge opening of diameter less than thediameter of said last chamber and greater than the diameter of thepassage through the next adjacent upstream restriction so as to mix saidstreams in their travel through said chambers.

17. A fuel mixing unit for burner assemblies comprising an elongatedopen-ended body having an entrance chamber arranged to receive streamsof air and fuel, mean for injecting streams of air and fuel into saidentrance chamber to its open end, said body including a plurality ofexpansion chambers of successively increased cross section downstreamfrom said entrance chamher, said chambers being of substantially equalvolume, and a plurality of constriction members between said chamberswhereby said streams are 'mixed in their travel through said chambers.

JOHN L. MHCFARLANE.

References Cited in the file of this patent UNITED STATES PATENTS NumberNumber Name Date Dennis May 13, 1902 Lindemann et a1. Feb. 8, 1916 ArmorFeb. 27, 1917 Mastenbrook Sept. 25, 1917 Schroeder Sept. 5, 1922 ZanderDec. 4, 1923 Argo et a1. May 7, 1929 Foster June 14, 1932 Methudy May16, 1933 Maxon, Jr Jan. 30, 1945 Focke et a1 Aug. 28, 1945 Clements Jan.29, 1946 FOREIGN PATENTS Country Date Great Britain of 1876 GermanySept. 24, 1900 Great Britain of 1909 France July 2, 1934

